A YC separating filter adaptive to a movement of an image judges whether an image is a still image or a moving image and performs a YC separation suitable for an image signal of the type judged. According to the current NTSC, composite signals in which C signals are frequency-multiplexed to a high frequency region of Y signals are employed. Therefore, YC separation is required in a receiver and an imperfect separation causes a deterioration in the quality of the image, such as cross color or dot crawl. Recently, with development of large capacity digital memory, various kinds of signal processing circuits for improving the quality of image, such as a YC separating filter adaptive to a movement of an image utilizing a delay circuit having a delay time equal to a vertical scanning frequency of a television signal or more, have been proposed.
FIG. 110 is a block diagram showing an example of a conventional YC separating filter adaptive to a movement of an image. In FIG. 110, video (V) signals 1101 of the NTSC type are input to an input terminal 1001 and applied to input terminals of an intra-field YC separating circuit 1004, an inter-frame YC separating circuit 1005, a Y signal movement detecting circuit 1006 and a C signal movement detecting circuit 1007.
In the intra-field YC separating circuit 1004, by an intra-field filter (not shown), intra-field YC separated Y signals 1102 and intra-field YC separated C signals 1103 are applied to a first input terminal of a Y signal mixing circuit 1009 and a first input terminal of a C signal mixing circuit 1010, respectively.
In addition, in the inter-frame YC separating circuit 1005, by an inter-frame filter (not shown), inter-frame YC separated Y signals 1104 and inter-frame YC separated signals 1105 are applied to a second input terminal of the Y signal mixing circuit 1009 and a second terminal of the C signal mixing circuit 1010, respectively.
On the other hand, signals 1106 showing the amount of movement of Y signals detected by the Y signal movement detecting circuit 1006 are applied to an input terminal composing circuit 1008 while signals 1107 showing the amount of movement of C signals detected by the C signal movement detecting circuit 1007 are applied to the other input terminal of the composing circuit 1008.
Movement detecting signals 1108 composed by the composing circuit 1008 are applied to a third input terminal of the Y signal mixing circuit 1009 and a third terminal of the C signal mixing circuit 1010. A movement detecting circuit 1080 comprises the Y signal movement detecting circuit 1006, the C signal movement detecting circuit 1007 and the composing circuit 1008.
Movement adaptive YC separated Y signals 1109, which are output from the Y signal mixing circuit 1009, are transferred to the output terminal 1002 and movement adaptive YC separated C signals 1110, which are output from the C signal mixing circuit 1010, are transferred to the output terminal 1003.
The operation of FIG. 110 will now be described. In the movement detecting circuit 1080, when the V signals are divided into Y signals and C signals, the composing circuit 1008 composes the output of the Y signal movement detecting circuit 1006 and the output of the C signal movement detecting circuit 1007 to judge that the V signals 1101 are either signals showing a still image or signals showing a moving image.
FIG. 111 shows the Y signal movement detecting circuit 1006 in detail. In FIG. 111, V signals 1101 are input to the input terminal 1011 and then signals obtained by delaying the V signals by one-frame in a one-frame delay circuit 1075 are subtracted from the V signals directly input by a subtracter 1076 to find a one-frame difference of the V signals 1101. Then, the one-frame difference is transferred to an absolute value circuit 1078 through a low-pass filter (LPF) 1077 and an absolute value thereof is found. The absolute value is converted to signals 1106, which show the amount of movement of low-pass component of Y signals, in a non-linear converting circuit 1079 and then output to the output terminal 1081.
In addition, FIG. 112 shows the C signal movement detecting circuit 1007 in detail. In FIG. 112, V signals 1101 are input to the input terminal 1011 and then signals obtained by delaying the V signals by two frames in a two-frame delay circuit 1082 are subtracted from the V signals directly input by a subtracter 1083 to find a two-frame difference of the V signals 1101. Then, the two-frame difference is transferred to an absolute value circuit 1085 through a band-pass filter (BPF) 1084 and an absolute value thereof is found. The absolute value is converted to signals 1107, which show the amount of movement of C signals, in a non-linear converting circuit 1086 and then output from the output terminal 1087.
The composing circuit 1008 selects a larger value between the amount of movement of Y signals 1106 and the amount of movement of C signals 1107 and outputs it. The result of the judgment is represented in the form of a movement factor k (0.ltoreq.k.ltoreq.1) and, for example, when the image is judged to be a perfect still image, k is equal to 0 and when the image is judged to be a perfect moving image, k is equal to 1. Then, it is transferred to the Y signal mixing circuit 1009 and the C signal mixing circuit 1010 as a control signal 1108.
Generally, when the image is a still image, the Y signals and the C signals are separated by performing inter-frame YC separation utilizing an inter-frame correlation.
FIG. 113 shows the inter-frame YC separating circuit 1005 in detail. In FIG. 113, V signals 1101 are input to the input terminal 1011 and signals obtained by delaying the V signals by one-frame in the one-frame delay circuit 1088 and the V signals directly input are added by an adder 1089 to find a one-frame sum. Thus obtained YF signals 1104 are output from the output terminal 1091 while the YF signals 1104 are subtracted from the V signals 1101 input from the input terminal 1011 by a subtracter 1090, whereby CF signals 1105 are obtained and output from the output terminal 1092.
When the image is a moving image, the Y signals and the C signals are separated by performing intra-field YC separation utilizing an intra-field correlation.
FIG. 114 shows the intra-field YC separating circuit 1004 in detail. In FIG. 114, V signals 1101 are input to the input terminal 1011 and signals obtained by delaying the V signals by one-line in the one-line delay circuit 1093 and the V signals directly input are added by an adder 1094 to find a one-line sum. Thus obtained Yf signals 1102 are output from the output terminal 1096 while the YF signals 1102 are subtracted from the V signals 1101 input from the input terminal 1011 by a subtracter 1095, whereby Cf signals 1103 are obtained and output from the output terminal 1097.
In the movement adaptive YC separating filter, the intra-field YC separating circuit 1004 and the inter-frame YC separating circuit 1005 are arranged in parallel and the Y signal mixing circuit 1009 performs the following operation in accordance with the movement factor k composed by the composing circuit 1008, whereby the movement adaptive YC separated Y signals 1109 are output from the output terminal 1002. EQU Y=kYf+(1-k)YF
wherein Yf is the intra-field YC separated Y signal output 1102 and YF is the inter-frame YC separated Y signal output 1104.
Similarly, the C signal mixing circuit 1010 performs the following operation in accordance with the control signal 1108, whereby the movement adaptive YC separated C signals 1110 are output from the output terminal 1003. EQU C=kCf+(1-k)CF
wherein Cf is the intra-field YC separated C signal output 1103 and CF is the inter-frame YC separated C signal output 1105.
In the movement adaptive YC separating filter, the C signal moving detecting circuit 1007 may be constructed as shown in FIG. 115. In FIG. 115, V signals 1101 are input from the input terminal 1011 and demodulated to two kinds of color difference signals R-Y and B-Y by a color demodulator 1098. These color difference signals R-Y and B-Y are time-shared and multiplexed at a prescribed frequency in the time-division multiplex circuit 1099 and delayed by two frames in the two-frame delay circuit 1082. Thereafter, the output of the two-frame delay circuit 1082 is subtracted from the output of the time division multiplex circuit 1099 by the subtracter 1083 to obtain a two-frame difference. Then, Y signal component is removed by passing the two-frame difference through the low-pass filter 1084 and an absolute value is obtained by the absolute value circuit 1085. Then, the absolute value is converted to signals showing the detected amount of movement of the C signals by the nonlinear conversion circuit 1086 and then output from the output terminal 1087.
FIG. 116 is a block diagram showing another movement adaptive YC separating filter. In FIG. 116, V signals 6201 of NTSC system are input to an input terminal 6001 and applied to input terminals of an intra-field Y signal extracting circuit 6004, an inter-frame Y signal extracting circuit 6005, a color demodulation circuit 6006 and a Y signal movement detecting circuit 6011.
In the color demodulation circuit 6006, the V signals are demodulated to two kinds of color-difference signals, i.e., R-Y signals and B-Y signals. These color-difference signals are time-shared and multiplexed at a prescribed frequency in the time-division multiplex circuit 6007. The output signals from the time-division multiplex circuit 6007 are band restricted by a low-pass filter (LPF) 6008 whose band pass is 1.5 MHz and below. The band-restricted color-difference frequency 6204 is applied to the intra-field C signal extracting filter 6009, the inter-frame C signal extracting filter 6010 and the C signal movement detecting circuit 6012.
In the intra-field C signal extracting filter 6009, the intra-field YC separated C signals 6205 are applied to a first input terminal of a C signal mixing circuit 6015. In addition, in the inter-frame C signal extracting filter 6010, the inter-frame YC separated C signals 6206 are applied to a second input terminal of a C signal mixing circuit 6015. On the other hand, signals 6207 showing the amount of movement of Y signals detected by the Y signal movement detecting circuit 6011 are applied to an input terminal of a composing circuit 6013 while signals 6208 showing the amount of movement of C signals detected by the C signal movement detecting circuit 6012 are applied to the other input terminal of the composing circuit 6013.
-Movement detecting signals 6209 composed by the composing circuit 6013 are applied to a third input terminal of the Y signal mixing circuit 6014 and a third input terminal of the C signal mixing circuit 6015. A movement detecting circuit 6080 comprises the Y signal movement detecting circuit 6011, the C signal movement detecting circuit 6012 and the composing circuit 6013. Movement adaptive YC separated Y signals 6210, which are output from the Y signal mixing circuit 6014, are transferred to the output terminal 6002 and movement adaptive YC separated C signals 6211, which are output from the C signal mixing circuit 6015, are transferred to the output terminal 6003.
The operation of the FIG. 116 circuit will be described. In the movement detecting circuit 6080, when the V signals are divided into Y signals and C signals, the composing circuit 6013 composes the output of the Y signal movement detecting circuit 6011 and the output of the C signal movement detecting circuit 6012 to judge that the V signals 6201 are either signals showing a still image or signals showing a moving image.
FIG. 117 shows the Y signal movement detecting circuit 6011 in detail. In FIG. 117, V signals 6201 are input to the input terminal 6021 and then signals obtained by delaying the V signals by one-frame in a one-frame delay circuit 6151 are subtracted from the V signals directly input by a subtracter 6152 to find a one-frame difference of the V signals 6201. Then, the one-frame difference is transferred to an absolute value circuit 6154 through a LPF 6153 whose band pass is 2.1 MHz and below and an absolute value thereof is found. The absolute value is converted to signals 6207, which show the movement of low-pass component of Y signals, in a non-linear converting circuit 6155 and output to the output terminal 6156.
In addition, FIG. 118 shows the C signal movement detecting circuit 6012 in detail. In FIG. 118, the band restricted color-difference signals 6204 are input to the input terminal 6023 and then signals obtained by delaying the color-difference signals by two frames in a two-frame delay circuit 6157 are subtracted from the color-difference signals 6204 directly input by a subtracter 6158 to find a two-frame difference of the color-difference signals 6204. Then, an absolute value of the two-frame difference is found in an absolute circuit 6159, and the absolute value is converted to signals 6208, which show the amount of movement of C signals, in a non-linear converting circuit 6160 and then output from the output terminal 6161.
The composing circuit 6013 selects a larger value between the amount of movement of Y signals 6207 and the amount of movement of C signals 6208 and outputs it. The result of the judgment is represented in the form of a movement factor k (0.ltoreq.k.ltoreq.1) and, for example, when the image is judged to be a perfect still image, k is equal to 0 and when it is judged to be a perfect moving image, k is equal to 1. Then, it is transferred to the Y signal mixing circuit 6014 and the C signal mixing circuit 6015 as control signals 6209.
Generally, when the image is a still image, the Y signals and the C signals are separated by performing YC separation using an the inter-frame Y signal extracting filter 6005 and the inter-frame C signal extracting filter 6010 utilizing an inter-frame correlation.
FIG. 119 shows the inter-frame Y signal extracting filter 6005 in detail. In FIG. 119, V signals 6201 are input to the input terminal 6021 and signals obtained by delaying the V signals by one frame in the one-frame delay circuit 6162 and the V signals directly input are added by an adder 6163 to find a one-frame sum. Thus obtained YF signals 6203 are output to the output terminal 6164.
FIG. 121 shows the inter-frame C signal extracting filter 6010 in detail. In FIG. 121, color-difference signals 6204 are input to the input terminal 6023 and signals obtained by delaying the color-difference signals 6204 by one frame in the one-frame delay circuit 6168 and the color-difference signals 6204 directly input are added by an adder 6169 to find a one-frame sum. Thus obtained YF signals 6203 are output to the output terminal 6170.
When the image is a moving image, the Y signals and the C signals are separated by performing YC separation using the intra-field Y signal extracting filter 6004 and the intra-field C signal extracting filter 6009 utilizing an intra-field correlation.
FIG. 120 shows the intra-field Y signal extracting filter 6004 in detail. In FIG. 120, V signals 6201 are input to the input terminal 6021 and signals obtained by delaying the V signals by one-line and the V signals directly input are added by an adder 6166 to find a one-line sum. Thus obtained Yf signals 6202 are output from the output terminal 6167.
FIG. 122 shows the intra-field C signal extracting filter 6009 in detail. In FIG. 122, color-difference signals are input to the input terminal 6023 and signals obtained by delaying the color-difference signals by one line in the one-line delay circuit 6171 and the color-difference signals 6204 directly input are added by an adder 6172 to find a one-line sum. Thus obtained Cf signals 6205 are output from the output terminal 6173.
In the movement adaptive YC separating filter, the intra-field Y signal extracting filter 6004 and the inter-frame Y Signal extracting filter 6005 are arranged in parallel and the Y signal mixing circuit 6014 performs the following operation in accordance with the control signal 6209, i.e., the movement factor k composed by the composing circuit 6013, whereby the movement adaptive YC separated Y signals 6210 are output from the output terminal 6002. EQU Y=kYf+(1-k)YF
wherein Yf is the intra-field YC separated Y signal output 6202 and YF is the inter-frame YC separated Y signal output 6203.
Similarly, the intra-field C signal extracting filter 6009 and the inter-frame C signal extracting filter 6010 are arranged in parallel and the C signal mixing circuit 6015 performs the following operation in accordance with the control signal 6209, whereby the movement adaptive YC separated C signals 6211 are output from the output terminal 6003. EQU C=kCf+(1-k)CF
wherein Cf is the intra-field YC separated C signal output 6205 and CF is the inter-frame YC separated C signal output 6206.
In the conventional YC separating filter adaptive to the movement of image shown in FIG. 110, the Yf signals obtained by the intra,field YC separating circuit 1004 and the YF signals obtained by the inter-frame YC separating circuit 1005 are mixed on the basis of the amount obtained by composing the amount of movement detected by the Y signal movement detecting circuit 1006 and the amount of movement detected by the C signal movement detecting circuit 1007. Similarly, the Cf signals obtained by the intra-field YC separating circuit 1004 and the CF signals obtained by the inter-frame YC separating circuit 1005 are mixed on the basis of the composed amount of movement.
In the YC separating filter adaptive to the movement of image shown in FIG. 116, the Yf signals obtained by the intra-field Y signal extracting filter 6004 and the YF signals obtained by the inter-frame Y signal extracting filter 6005 are mixed on the basis of the amount obtained by composing the amount of movement detected by the Y signal movement detecting circuit 6011 and the amount of movement detected by the C signal movement detecting circuit 6012. Similarly, the Cf signals obtained by the intra-field C signal extracting filter 6009 and the CF signals obtained by the inter-frame C signal extracting filter 6010 are mixed on the basis of the composed amount of movement.
In the above-described conventional examples, the filter characteristic in the still image is completely different from that in the moving image, so that the resolution changes when the image changes from the still image to the moving image or from the moving image to the still image, with the result that the quality of the image deteriorates while processing the moving image.